Rolling-lobe flexible members of air springs have proven effective to a great extent, for example, as vehicle suspensions especially for suspending the wheel axles of trucks and buses. The rolling-lobe flexible members are attached at a first end to a roll-off piston which is usually made of metal or plastic. In the operating state, the piston moves within the rolling-lobe flexible member which folds outside in and forms a rolling lobe which rolls on the outer surface of the roll-off piston.
The reinforcement arrangement takes up forces which arise because of the overpressure in the rolling-lobe flexible member of the air spring. In air spring flexible members, the cord fabric layer preferably comprises fully synthetic fibers such as polyamide. The so-called cord fabric is manufactured from the cord threads and is made of a multiplicity of cord threads in warp direction lying parallel next to each other. The cord threads are held loosely together at greater spacings by a few thin threads in the weft direction. This cord fabric layer is rubberized with a suitable rubber mixture such as a polychloroprene mixture and, after being cut at an angle, four or six layers are built into the air spring rolling-lobe flexible member so that the cords lie crosswise. Depending upon the type of air spring, the cord threads of the two cord fabric sheets each have a winding angle of approximately 40° to 80° referred to the peripheral direction. For the commercial mass manufacture, it is important that the angles of all fabric layers are mirror symmetrical with respect to the peripheral direction. Accordingly, if one fabric layer defines an angle of, for example, 60° with respect to the peripheral direction, then the fabric layer which crosses this fabric layer must also form an angle of 60° with the peripheral direction. The first winding angle is formed in the clockwise direction and the second winding angle is formed in the counterclockwise direction with both being from the peripheral direction.
Most air spring rolling-lobe flexible members for motor vehicles are manufactured with two mutually crossing fabric layers in order to achieve a high flexibility of the flexible member wall of the air spring rolling-lobe flexible member. As a consequence of increasing commercial loads of motor vehicles and ever smaller structural spaces for mounting, present day air springs must withstand ever higher pressures, for example, in the region of 10 bar or more. In order to be able to withstand higher operating pressures, it would be conceivable to arrange four or six cord fabric layers in the flexible member wall. Because of the small structural size of the air spring rolling-lobe flexible member, the strengthening reinforcement arrangement must, however, be very thin because a very small roll-off radius must be present.
In the roll-off radius, a higher tensile load occurs in the fabric layer, which comes to lie outwardly, than in the inner fabric layer because of the spacing of the fabric layers. At high pressures, this can lead to the condition that, for example, in a two layer reinforcement arrangement, the total air spring load is carried only by the outer fabric layer and the inner fabric layer no longer contributes. This leads to a serious reduction of the bursting pressure of the flexible member and to an extreme shortening of the service life.
U.S. Pat. No. 5,566,929 describes an air spring rolling-lobe flexible member wherein the service life is intended to be improved by utilizing a reinforcement arrangement having three fabric layers. The build-up of these three fabric layers is symmetrical to the center of the reinforcement arrangement. The middle fabric layer has a strength which corresponds to the sum of the two strengths of the outer fabric layers. The outer fabric layers are arranged symmetrically to the middle layer and have the same reinforcement. With the use of three fabric layers, the bonding surface between rubber layers and fabric layers is increased which leads to an improved service life.
The disadvantage described initially herein that the outer fabric layer, because of the bending of the flexible member in the rolling-lobe, experiences a greater strain or elongation than the layers which lie further inwardly, and therefore must take up proportionally more force, is, however, not eliminated by this configuration.